1. Field of the Invention
The present invention relates to a method for manufacturing two epitaxially-grown sapphireless substrates of Group III nitrogen compound semiconductor at one time, the substrates produced by the method, and the manufacture of a LED utilizing the substrates so-produced.
2. Description of the Related Art
It has been known that a gallim nitride (GAN) compound semiconductor may be used to obtain a light-emitting diode (LED) that emits blue light. This semiconductor is useful because of its high luminous efficiency resulting from direct electron transition and its ability to emit blue light, which is one of the three primary colors.
A Group III nitrogen compound semiconductor satisfying the formula Al.sub.x Ga.sub.y In.sub.1-x-y N, inclusive of x=0, y=0, and x=y=0, is also used in LEDS material that emit light in the entire visible short wavelength and ultraviolet regions. This semiconductors is useful because it has an energy band gap equivalent to the wavelength of 200 to 650 nm and has a direct electron transition characteristic.
It, however, has been difficult to produce bulk single crystalline Group III nitride compound semiconductor because the equilibrium vapor pressure of the nitrogen, as one of the components, is extremely high at the growth temperature of the semiconductor. Therefore, the Group III nitride compound semiconductor grown epitaxially on a sapphire substrate has always been used. Namely, the LED employing the semiconductor is always being used with a sapphire substrate resulting in a structural constraint in forming the electrodes, light emission inefficiency and so on, because of the sapphire substrate.
In actuality, electrodes for an n-layer and a p-layer cannot sandwich those layers because the substrate is insulative. Therefore, the electrodes for those layers have been formed only on a surface layer of the LED. This structural constraint has inevitably required additional manufacturing processes to form a groove which insulates these two electrodes from each other and a hole in which the electrode for either a lower layer of the two, the p-layer or the n-layer, is formed.
Further, the LED with this structure requires feed currents to the lower layer in parallel to its surface. Consequently, the resistivity of the LED becomes undesirably high, enlarging the voltage drop, and increasing the Joule heat energy expended by the device.
A single crystalline ZnO layer has been used as a buffer layer that helps grow the Group III nitride compound semiconductors with the fine crystallinity on the sapphire substrate mitigating lattice differences. However, luminous intensity of the conventional LED is not as good as expected in spite of the fine crystallinity of each layer and the lattice match between the sapphire substrate and the ZnO buffer layer, and between the ZnO layer and the Group III nitride compound semiconductor.